refactor: organize backend by business responsibility

src/modules/banking/bank-cards/domain/rub-money.spec.ts

@@ -0,0 +1,57 @@
+import { parseRubMoney, rubMoney } from './rub-money';
+
+describe('RUB money', () => {
+  it.each([
+    ['0', 0n],
+    ['-100', -10000n],
+    ['0.01', 1n],
+    ['123.4', 12340n],
+    ['90071992547409.93', 9007199254740993n],
+    ['92233720368547758.07', 2n ** 63n - 1n],
+    ['-92233720368547758.08', -(2n ** 63n)],
+  ])('roundtrips %s exactly', (value, kopecks) => {
+    expect(parseRubMoney({ currency: 'RUB', value })).toBe(kopecks);
+    expect(rubMoney(kopecks)).toEqual({ currency: 'RUB', value });
+  });
+
+  it.each([
+    '92233720368547758.08',
+    '-92233720368547758.09',
+    '1.001',
+    '1.000',
+    'NaN',
+    'Infinity',
+    '1e2',
+    '1,23',
+    '',
+    ' 1',
+    '1\n',
+    '01',
+  ])('rejects invalid input %s without rounding', (value) => {
+    expect(() => parseRubMoney({ currency: 'RUB', value })).toThrow();
+  });
+
+  it('rejects other currencies and non-string values', () => {
+    expect(() => parseRubMoney({ currency: 'USD', value: '1' })).toThrow();
+    expect(() =>
+      parseRubMoney({ currency: 'RUB', value: 1 as unknown as string }),
+    ).toThrow();
+  });
+
+  it('requires positive operation amounts, including at the maximum', () => {
+    for (const value of ['0', '-0.00', '-0.01'])
+      expect(() => parseRubMoney({ currency: 'RUB', value }, true)).toThrow();
+    expect(parseRubMoney({ currency: 'RUB', value: '0.01' }, true)).toBe(1n);
+    expect(
+      parseRubMoney({ currency: 'RUB', value: '92233720368547758.07' }, true),
+    ).toBe(2n ** 63n - 1n);
+  });
+
+  it('formats computed sums beyond the storage range without losing precision', () => {
+    expect(rubMoney(2n * (2n ** 63n - 1n))).toEqual({
+      currency: 'RUB',
+      value: '184467440737095516.14',
+    });
+    expect(rubMoney(-1n)).toEqual({ currency: 'RUB', value: '-0.01' });
+  });
+});